1. Technical Field
The present disclosure relates to a device and a method of protection from noise that is present in a digital signal.
2. Description of the Related Art
FIG. 1 shows a continuous-time differential comparator 1 of a known type. The comparator 1 is configured for accepting at input an analog input signal Vin and supplying at output a comparison signal Vcomp, of a binary type, which can assume a high logic value VcompH (logic 1) or a low logic value VcompL (logic 0) on the basis of the analog input signal Vin.
In greater detail, the comparator 1 receives on an inverting input and on a non-inverting input the analog input signal Vin. In use, the comparator 1 compares the voltage signal VinP present on the non-inverting input with the voltage signal VinN present on the inverting input, and supplies at output the comparison signal Vcomp according to the following formula (1):
                    {                                                            Vcomp                =                                  Vcomp                  L                                                                    if                                                                        Vin                  P                                <                                  Vin                  N                                                                                                        Vcomp                =                                  Vcomp                  H                                                                    if                                                                        Vin                  P                                <                                  Vin                  N                                                                    }                            (        1        )            
It is clear that, whereas the voltage signals VinP and VinN are analog signals, the comparison signal Vcomp is of a binary type, since it assumes alternatively the high logic value VcompH and the low logic value VcompL.
Defining the analog input signal Vin as differential signal Vin=VinP−VinN the equations of formula (1) can be expressed according to the following formula (2):
                    {                                                            Vcomp                =                                  Vcomp                  L                                                                    if                                                                        Vin                  P                                <                0                                                                                        Vcomp                =                                  Vcomp                  H                                                                    if                                                                        Vin                  P                                >                0                                                    }                            (        2        )            
FIG. 2a shows an analog input signal Vin of a sinusoidal type, represented showing the voltage signals VinP and VinN at the inputs of the comparator 1, which oscillates assuming the voltage values (−Vs, . . . , +Vs), whilst FIG. 2b shows the comparison signal Vcomp, which assumes the logic value VcompH=1 or VcompL=0 according to the equation expressed by the formula (2).
The analog input signal Vin generally comprises a useful signal component and a noise component. The noise component may in turn be broken down into an electronic-noise component and in an impulsive-noise component. For example, noise caused by capacitive couplings, often associated with switched-capacitor circuit structures, causes brief and sudden voltage peaks (referred to as “glitches”), generally of a periodic type, when there is a switching of digital signals present in the switched-capacitor structures.
As is shown in FIGS. 2a and 2b, the presence of numerous events of impulsive noise 5 (for example, glitches) in rapid succession with respect to one another in the analog input signal Vin can cause respective noise switchings 6 of spurious and undesirable noise, which also occur in rapid succession with respect to one another, in the comparison signal Vcomp of the comparator 1.
These noise switchings 6 can cause improper operation of a system in which the comparator 1 is implemented. For instance, if the output voltage signal of the comparator 1 is used as input of a phase-locked-loop (PLL) circuit, for example of a feedback circuit that operates synchronously, the noise switchings could jeopardize proper operation of the PLL circuit and consequently of the entire system.